Add note about production deployments.

Fixes #11511.

Author: steveklabnik

src/doc/complement-lang-faq.md

@@ -1,6 +1,5 @@
 % Language FAQ
 
-
 ## Are there any big programs written in it yet? I want to read big samples.
 
 There aren't many large programs yet. The Rust [compiler][rustc], 60,000+ lines at the time of writing, is written in Rust. As the oldest body of Rust code it has gone through many iterations of the language, and some parts are nicer to look at than others. It may not be the best code to learn from, but [borrowck] and [resolve] were written recently.
@@ -29,6 +28,18 @@ You may also be interested in browsing [GitHub's Rust][github-rust] page.
 
 [github-rust]: https://github.com/trending?l=rust
 
+## Is anyone using Rust in production?
+
+Currently, Rust is still pre-1.0, and so we don't recommend that you use Rust
+in production unless you know exactly what you're getting into.
+
+That said, there are two production deployments of Rust that we're aware of:
+
+* [OpenDNS](http://labs.opendns.com/2013/10/04/zeromq-helping-us-block-malicious-domains/)
+* [Skylight](http://skylight.io)
+
+Let the fact that this is an easily countable number be a warning.
+
 ## Does it run on Windows?
 
 Yes. All development happens in lock-step on all 3 target platforms. Using MinGW, not Cygwin. Note that the windows implementation currently has some limitations: in particular 64-bit build is [not fully supported yet][win64], and all executables created by rustc [depend on libgcc DLL at runtime][libgcc].